In-situ synthesis of reactive hydroxyapatite nano-crystals for a novel approach of surface grafting polymerization

A novel approach to surface modification of hydroxyapatite (HAp) nano-crystals was described based on in-situ synthesis of surface thiol-functionalized HAp (HAp-SH) and subsequent grafting polymerization of ethylene glycol methacrylate phosphate (EGMP). Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses showed that thiol groups were introduced on HAp surfaces by adding 3-mercaptopropionic acid during hydrothermal synthesis of HAp nano-crystals. The radical chain transfer to surface thiol groups generated the sulfur-centered radicals on HAp nano-surfaces, which initiated the surface grafting polymerization of EGMP. Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD) analyses confirmed the grafting reaction on HAp surfaces. Zeta potentials of control HAp, thiol-functionalized HAp (HAp-SH), and PolyEGMP-grafted HAp in phosphate buffered saline (PBS) solutions (pH 7.4) were negative and decreased with increasing the amount of grafted PolyEGMP. TEM measurements and time-dependent phase monitoring suggested that the colloidal stability of PolyEGMP-grafted HAp over synthesized HAp nano-crystals in water dramatically increased without inter-crystal aggregation.